This invention relates to moisture measuring apparatus, and more particularly, to apparatus for the high speed monitoring of the moisture content of grain or the like.
Excessive moisture in bulk food grain enhances the growth of poisonous molds, and stimulates oxidation which produces heat sufficient to cause spontaneous combustion. Therefore, there is a need to monitor the moisture content of bulk food grains both during storage and in transit. In one method presently used to measure the moisture content of bulk grains, small samples are collected from large storage facilities and these samples are then analyzed in a laboratory using standard physical and chemical methods. This method is extremely limited in terms of reliability of the sample. Further, this method does not afford continuous monitoring of the moisture in the bulk grain.
This invention provides for continuous monitoring of the bulk grain by means of electromagnetic radiation. During handling, bulk grain shipments usually are handled on conveyor belts or are gravity dispensed from hoppers into mail cars on tracks. In either case, it is relatively easy to pass the material through a continuous reading measurement system or port. The examination system hereof essentially comprises a transmit and receive antenna, capable of transmitting two separate frequencies through the bulk grain as it is carried by on a conveyor belt, or falls through a test port during dispensing from a storage hopper. Electromagnetic attenuation at VHF and UHF frequencies is found to be almost totally caused by the residual moisture in food grains. Systems for measuring moisture by means of electromagnetic radiation are known in the prior art. Examples of such systems are disclosed in the following U.S. Patents: U.S. Pat. No. 3,851,244 to Mounce; U.S. Pat. No. 3,694,737 to Busker et al.; U.S. Pat. No. 3,693,079 to Walker; and U.S. Pat. No. 3,498,122 to Howard.
In said U.S. Pat. No. 3,851,244 to Mounce, a rather complex microwave system is disclosed. Said U.S. Pat. No. 3,694,737 to Busker et al. discloses a microwave moisture measuring system in which the transmission path is changed by at least one-half wavelength. Said U.S. Pat. No. 3,693,079 to Walker discloses moisture measuring apparatus which utilizes a microwave signal and a penetrating signal such as x-rays or beta rays, and said U.S. Pat. No. 3,498,112 to Howard discloses a microwave system in which two separate transmitters and receivers are provided.
The apparatus of this invention also uses microwave energy to measure moisture and is primarily designed to measure the moisture content of bulk grain. The system of this invention is not a complex system. The system includes a single transmitter capable of transmitting two frequencies, a receiver, and signal processing circuitry.